1. Field of the Invention
The present invention relates to a polishing pad for precisely and rapidly polishing a surface of a semiconductor wafer, including a wafer of an element semiconductor such as silicon and a compound semiconductor such as gallium arsenide, indium phosphide and gallium phosphide, the polishing pad having a high resistance to a corrosive etchant.
2. Description of Related Art
Conventionally, semiconductor wafers are polished by a polishing pad while supplying a polishing solution adopted for a particular semiconductor. The polishing pad includes a velour-type pad in which polyurethane resin is impregnated into a polyester nonwoven fabric and a suede-type pad in which a foamed polyurethane layer is formed on a base of a polyester nonwoven fabric.
The polishing solution used for polishing a semiconductor wafer includes a mechanochemical polishing slurry and a chemical polishing solution. The mechanochemical polishing slurry comprises abrasives and a polishing accelerator (hereinafter referred to as "etchant") and the chemical polishing solution comprises only an etchant and not abrasives. An etchant is used in both types of polishing solutions and a highly active or reactive and corrosive etchant is required for polishing a semiconductor wafer, for example, a bromine-methanol-based etchant, a hypochlorous acid-based etchant, and an amine-based etchant.
When using a highly active and corrosive etchant (hereinafter referred to as "a corrosive etchant") for polishing a semiconductor wafer, a polishing pad of either the velour-type or suede-type is corroded and the chemical and mechanical structures thereof deteriorated. As a result, the efficiency of the polishing pad is decreased, including a reduced polishing rate, an increased surface roughness, and an undulation of a polished wafer, and damage occurs to a wafer. The life time of a polishing pad is shortened when using a corrosive etchant, in comparison with using a polishing solution which is not corrosive, and it is an economical disadvantage that an expensive polishing pad must be frequently replaced by a new pad. Even when using an etchant having relatively low corrosiveness, a velour-type or suede-type pad is gradually deteriorated by the etchant over a lapse of time, and even though the pad is deteriorated, only slightly, the conditions for polishing such as a supply of an etchant, a working pressure, a rotation speed of a polishing plate, and a temperature and a flow rate of a cooling water for a polishing plate must be continuously controlled, to cope with the degree of deterioration of the pad over a period of time, to obtain a desired polished surface of a semiconductor wafer.
As described above, both velour-type and suede-type pads currently available have a low resistance to a corrosive etchant and thus have problems of polishing efficiency, workability, cost or economy.
Therefore, the main object of the present invention is to provide a polishing pad for a semiconductor wafer, which pad has an excellent polishing efficiency and a high resistance against a corrosive etchant, allowing a high polishing efficiency even after a long period of polishing with the corrosive etchant.